A freely rotatable spinning ring having air-bearings for generally friction-free support thereof may be rotated by the frictional drag of a yarn traveler mounted on the ring as yarn is simultaneously twisted or spun and wound onto a yarn carrier or bobbin rotating inside the ring. The traveler rotates about the axis of the yarn carrier at a rotational speed only slightly less than that of the yarn carrier, the difference in speeds allowing the yarn fed to the yarn carrier to be wound thereon under generally uniform tension while compensating for differences in the winding-on diameter of the yarn package being built on the yarn carrier.
In conventional stationary spinning ring apparatus a practical limit on production speeds, or critical speed, is reached when the linear speed of the traveler orbiting the stationary ring is in the neighborhood of 5000 feet per minute. Above that speed, the friction of the traveler on the ring becomes so great that frictional heat tends to burn up the traveler, and the friction becomes erratic as well, tending to overstress and break the yarn.
By allowing the ring to rotate freely on very low friction bearings, the frictional force between traveler and ring causes the ring to rotate at a speed generally approximating that of the traveler, so that while the traveler will have some sliding motion on the ring (thereby compensating for short-term variations in winding-on speeds), the average linear sliding speed will be very low, thereby practically eliminating wear between ring and traveler and causing the frictional forces therebetween to be much more even with a resultant reduction in yarn breaks. Also, the yarn carrier can be rotated at much higher speeds, generally limited only by the mechanical capabilities of the bearings and drive for the rotating spindles on which the yarn carrier is mounted.
The advantages of freely rotating spinning rings are well known to those skilled in the art, as are the problems associated therewith, the principal problems being those of (a) achieving a balanced air flow to and within the radial and annularly axial (or cylindrical) air-bearings provided for each ring, and (b) preventing yarn tangling and breaking when the spindle drive is cut-off and spindle and ring are coasting to a stop at undesirable relative deceleration rates.
Prior art air-bearings for spinning rings have included multiple small holes disposed in the bearing walls for distributing air thereto from surrounding air chambers, and in some cases the small holes have been the porosity in sintered metal porous annular elements forming portions of the air-bearing structure. Such small holes tend to become stopped-up periodically or accidentally and may have peculiar non-uniform air distribution tendencies even when open, and these tendencies may be compounded when both cylindrical and radial air-bearings are supplied together by small holes in the cylindrical bearing walls. Where only a few small holes equally spaced around an air bearing are used to admit air (4, 8, and 16 holes are typical of the prior art patents mentioned hereinafter), it is probable that the full area of the air bearing surfaces is not being used efficiently, and that higher air pressure must be used to center and support the rotating ring member by means of the concentrated areas around the small holes where the air pressure is concentrated than if the full air-bearing surfaces were being used efficiently. Also, tiny particles of dirt or trash which inevitably turn up in compressed air systems may enter through the small air inlet holes and be dragged annularly around the air-bearing to jam in the solid bearing surfaces between the holes.
Air-bearing spinning rings in the prior art have had such low friction and high inertial forces that, once rotating, they tend to coast for extended periods of time, generally for longer periods of time than the spindles and yarn carriers of the spinning apparatus, after driving power is cut off. Therefore, the traveler on the rotating ring may rotate faster than the carrier toward the close of such periods of time, causing loss of yarn tension control as the yarn unwinds from the carrier and tangles and breaks.
In some cases, the air supply to the air-bearings of the rotating ring has been cut-off simultaneously with the power drive for the spindles and carriers, and then the ring has tended to decelerate so quickly that the aforementioned 5000 foot per minute critical speed of the traveler relative to the ring is reached before the carrier rotational speed has decelerated sufficiently to preclude such a condition.
U.S. Pat. Nos. 3,324,643, 3,481,131, and 4,023,342 disclose in detail the principles and prior art practices of yarn spinning or twisting with traveler-equipped freely rotating air-bearing spinning rings discussed above; however it is believed that there is no such equipment commercially available in the United States at this time. U.S. Pat. Nos. 950,507, 3,494,120, 3,611,697, 3,664,112, 3,851,448, 4,028,873, 4,030,282, 4,051,657, and 4,095,402 also disclose material useful in understanding the prior art.
On the basis of experiments with a working model, it appears that the present invention provides effective means for providing uniform air distribution within the radial and cylindrical air-bearings, for providing suitably balanced air distribution between the radial and cylindrical bearings, and for causing the rotating ring to decelerate in desired relation to the spindle, carrier, and traveler (upon cutting-off their driving power) to maintain suitable tension in the yarn throughout the deceleration. The means provided by the present invention for overcoming the technical problems and allowing trouble-free operation are so simple and effective that they should permit a practical initial cost and low maintenance costs during production spinning or twisting, thereby assuring commercial success through application of the apparatus to a large number of existing spinning and twisting spindles in the United States. It is believed that production increases in the order of 50% to 100% may be achieved at a cost of 30%, or less, of the cost of new equipment, and a reduction in mill space and operating personnel will also be realized as compared with adding machinery of conventional construction to achieve corresponding production increases.